1.概述
在Reactor单线程版本的设计中，I/O任务乃至业务逻辑都由Reactor线程来完成，这无疑增加了Reactor线程的负担，高负载情况下必然会出现性能瓶颈。此外，对于多处理器的服务器来说，单个Reactor线程也发挥不了多CPU的最大功效。下面我们对之前单线程版的Reactor进行改进。
改进方向
- 接受客户端连接请求的不在是单个线程-Acceptor，而是一个NIO线程池。
- I/O处理也不再是单个线程处理，而是交给一个I/O线程池进行处理。
其实改进方向很明确：就是针对可能的系统瓶颈，由单线程改进为多线程处理。这样的方案带来的好处显而易见，增加可靠性的同时也发挥多线程的优势，在高负载的情况下能够从容应对。
Key Word
Java NIO 事件驱动 主从Reactor模型
2.code未动，test先行
首先定义服务端用于处理请求的Handler，通过实现ChannelHandler接口完成。
代码语言：javascript复制public class SimpleServerChannelHandler implements ChannelHandler {
private static Logger LOG = LoggerFactory.getLogger(SimpleServerChannelHandler.class);
//记录接受消息的次数
public volatile int receiveSize;
//记录抛出的异常
public volatile Throwable t;
@Override
public void channelActive(NioChannel channel) {
if(LOG.isDebugEnabled()){
LOG.debug("ChannelActive");
}
}
@Override
public void channelRead(NioChannel channel, Object msg) throws Exception {
ByteBuffer bb = (ByteBuffer)msg;
byte[] con = new byte[bb.remaining()];
bb.get(con);
String str = new String(con,0,con.length);
String resp = "";
switch(str){
case "request1":resp = "response1";break;
case "request2":resp = "response2";break;
case "request3":resp = "response3";break;
default :resp = "Hello Client";
}
ByteBuffer buf = ByteBuffer.allocate(resp.getBytes().length);
buf.put(resp.getBytes());
receiveSize ;
channel.sendBuffer(buf);
}
@Override
public void exceptionCaught(NioChannel channel, Throwable t)
throws Exception {
this.t = t;
channel.close();
}
}Junit测试用例，setUp用于启动Server端和Client端。
代码语言：javascript复制public class ReactorTest extends BaseTest{
private static final Logger LOG = LoggerFactory.getLogger(ReactorTest.class);
private static String HOST = "localhost";
private static int PORT = 8888;
private static Client client;
private static Server server;
static SimpleServerChannelHandler h;
@BeforeClass
public static void setUp() throws Exception {
startServer();
startClient();
}
private static void startServer() throws Exception{
server = new Server();
ReactorPool mainReactor = new ReactorPool();
ReactorPool subReactor = new ReactorPool();
h = new SimpleServerChannelHandler();
server.reactor(mainReactor, subReactor)
.handler(h)
.bind(new InetSocketAddress(HOST,PORT));
}
private static void startClient() throws SocketException{
client = new Client();
client.socket().setTcpNoDelay(true);
client.connect(
new InetSocketAddress(HOST,PORT));
}
@Test
public void test() {
LOG.info("Sucessful configuration");
}
@Test
public void testBaseFunction(){
LOG.debug("testBaseFunction()");
String msg ="Hello Reactor";
ByteBuffer resp = client.syncSend(ByteBuffer.wrap(msg.getBytes()));
byte[] res = new byte[resp.remaining()];
resp.get(res);
Assert.assertEquals("Hello Client", new String(res,0,res.length));
}
@Test
public void testMultiSend(){
int sendSize = 1024;
for(int i = 0; i < sendSize; i ){
ByteBuffer bb = ByteBuffer.wrap("Hello Reactor".getBytes());
ByteBuffer resp = client.syncSend(bb);
byte[] res = new byte[resp.remaining()];
resp.get(res);
Assert.assertEquals("Hello Client", new String(res,0,res.length));
}
Assert.assertEquals(sendSize, h.receiveSize);
}
@Test
public void testTooLongReceivedByteSizeEexception(){
LOG.debug("testTooLongReceivedByteSizeEexception()");
int threshold = 1024;
byte[] dest = new byte[threshold 1];
Random r = new Random();
r.nextBytes(dest);
client.syncSend(ByteBuffer.wrap(dest));
Assert.assertEquals(IllegalArgumentException.class, h.t.getClass());
Assert.assertEquals("Illegal data length, len:" (threshold 1), h.t.getMessage());
}
@AfterClass
public static void tearDown() throws Exception {
server.close();
client.close();
}
}一共进行三项基本测试：
testBaseFunction
实现了基本发送接收消息的功能。
testMultiSend
重复发送消息，并且记录消息收发的次数。
testTooLongReceivedByteSizeEexception
测试server端在接收到异常码流的情况下，是否抛出异常。
3.设计及实现
3.1 Reactor和ReactorPool
Reactor作用就是不断进行轮询并检查是否有已经就绪的事件，如果有，那么就将事件分发给对应的Handler进行处理。这个角色其实就是NIO编程中的多路复用器java.nio.channels.Selector。因此，Reactor聚合一个Selector类型成员变量。轮询的过程如下：
代码语言：javascript复制public class Reactor extends Thread{
//...
private Selector selector;
private volatile boolean isShutdown;
Reactor(){
try {
selector = Selector.open();
} catch (IOException e) {
throw new RuntimeException("failed to open a new selector", e);
}
}
@Override
public void run() {
for(;;){
try {
getSelector().select(wakenUp);
Set<SelectionKey> keys;
synchronized(this){
keys = getSelector().selectedKeys();
}
Iterator<SelectionKey> it = keys.iterator();
while(it.hasNext()){
SelectionKey key = it.next();
processSelectedKey(key);
it.remove();
}
if(isShutdown()){
break;
}
} catch (Throwable e) {
LOG.warn("Unexpected exception in the selector loop.", e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) { }
}
}
}
}processSelectedKey(key)中进行的就是根据就绪事件key.readyOps()进行相应操作：
代码语言：javascript复制 private void processSelectedKey(SelectionKey key){
try {
NioChannel nioChannel = (NioChannel)key.attachment();
if (!nioChannel.isOpen()) {
LOG.warn("trying to do i/o on a null socket");
return;
}
int readyOps = key.readyOps();
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
nioChannel.sink().doRead();
}
if((readyOps & SelectionKey.OP_WRITE) != 0){
nioChannel.sink().doSend();
}
if((readyOps & SelectionKey.OP_CONNECT) != 0){
//remove OP_CONNECT
key.interestOps((key.interestOps() & ~SelectionKey.OP_CONNECT));
}
}catch (Throwable t) {
if (LOG.isDebugEnabled()) {
LOG.debug("Throwable stack trace", t);
}
closeSocket();
}
}这里的NioChannel是抽象类，是对NIO编程中的Channel语义的抽象（后面会有分析）。
此外，Reactor肯定要提供一个注册接口啦。。。
代码语言：javascript复制 public SelectionKey register(final NioChannel sc, final int interestOps, Object attachment){
if(sc == null){
throw new NullPointerException("SelectableChannel");
}
if(interestOps == 0){
throw new IllegalArgumentException("interestOps must be non-zero.");
}
SelectionKey key;
try {
key = sc.channel().register(getSelector(), interestOps, attachment);
} catch (ClosedChannelException e) {
throw new RuntimeException("failed to register a channel", e);
}
return key;
}ReactorPool是一个Reactor的线程池，这里就通过简单的数组形式进行模拟：
代码语言：javascript复制public class ReactorPool {
private static final Logger LOG = LoggerFactory.getLogger(ReactorPool.class);
private Reactor[] reactors;
private AtomicInteger index = new AtomicInteger();
//线程数默认为CPU数*2
private final int DEFAULT_THREADS = Runtime.getRuntime().availableProcessors() * 2;
public ReactorPool (){
this(0);
}
public ReactorPool(int nThreads){
if(nThreads < 0){
throw new IllegalArgumentException("nThreads must be nonnegative number");
}
if(nThreads == 0){
nThreads = DEFAULT_THREADS;
}
reactors = new Reactor[nThreads];
for(int i = 0; i < nThreads; i ){
boolean succeed = false;
try{
reactors[i] = new Reactor();
succeed = true;
}catch(Exception e){
throw new IllegalStateException("failed to create a Reactor", e);
}finally{
if (!succeed) {
for (int j = 0; j < i; j ) {
reactors[j].close();
}
}
}
}
}
public Reactor next(){
return reactors[index.incrementAndGet() % reactors.length];
}
public void close(){
for(int i = 0; i < reactors.length; i ){
reactors[i].setShutdown(true);
reactors[i].close();
}
}
}3.2 NioChannel和NioChannelSink
在进行Java原生Nio编程的过程中，会涉及到两种类型的Channel：
- java.nio.channels.SocketChannel
- java.nio.channels.ServerSocketChannel
其分别作为客户端和服务端调用接口。为了统一其公共行为，这里抽象出一个抽象类NioChannel，其成员组成如下：
- 聚合一个SelectableChannel类型（SocketChannel和ServerSocketChannel的公共父类）的成员变量。
- 持有一个所属Reactor对象的引用
- 聚合一个NioChannelSink类型成员变量。
NioChannelSink是将NioChannel的底层读写功能独立出来。一方面使NioChannel避免集成过多功能而显得臃肿，另一方面分离出底层传输协议，为以后底层传输协议的切换做准备。（TCP vs UDP，NIO、OIO、AIO）从这种意义上说，NioChannel取名为Channel貌似更合理。
代码语言：javascript复制public abstract class NioChannel {
protected Reactor reactor;
protected SelectableChannel sc;
protected SelectionKey selectionKey;
private NioChannelSink sink;
protected volatile ChannelHandler handler;
public NioChannel(SelectableChannel sc, int interestOps){
this.sc = sc;
try {
sc.configureBlocking(false);
} catch (IOException e) {
e.printStackTrace();
}
sink = nioChannelSink();
}
protected void fireChannelRead(ByteBuffer bb){
try {
handler.channelRead(this, bb);
} catch (Exception e) {
fireExceptionCaught(e);
}
}
protected void fireExceptionCaught(Throwable t){
try {
handler.exceptionCaught(this, t);
} catch (Exception e) {
e.printStackTrace();
}
}
//。。。
public abstract NioChannelSink nioChannelSink();
public interface NioChannelSink{
void doRead();
void doSend();
void sendBuffer(ByteBuffer bb);
void close();
}
}再来分析下NioChannel需要提供哪些功能：
首先，NIO编程中SocketChannel或ServerSocketChannel需要注册到多路复用器Selector中。那么这里就抽象成了NioChannel和Reactor的交互。
代码语言：javascript复制public void register(Reactor reactor, int interestOps){
this.reactor = reactor;
try {
selectionKey = sc.register(reactor().getSelector(), interestOps, this);
} catch (ClosedChannelException e) {
e.printStackTrace();
}
}这里将NioChannel对象作为附件，在Reactor中心轮询到ready事件后，会根据事件的类型（OP_ACCEPT OP_READ等），从SelectionKey中取出绑定的附件NioChannel
代码语言：javascript复制NioChannel nioChannel = (NioChannel)key.attachment();然后根据进行key.readyOps()做相应操作。这在Reactor中已经做过分析。
其次，作为Channel肯定要提供绑定bind和连接connect的功能了：
代码语言：javascript复制public abstract void bind(InetSocketAddress remoteAddress) throws Exception;
public abstract void connect(InetSocketAddress remoteAddress) throws Exception;这里用抽象方法是要将实现交由子类来完成。
最后，是用户通过NioChannel发送的消息的函数：
代码语言：javascript复制public void sendBuffer(ByteBuffer bb){
sink().sendBuffer(bb);
}
protected final void enableWrite(){
int i = selectionKey.interestOps();
if((i & SelectionKey.OP_WRITE) == 0){
selectionKey.interestOps(i | SelectionKey.OP_WRITE);
}
}
protected final void disableWrite(){
int i = selectionKey.interestOps();
if((i & SelectionKey.OP_WRITE) == 1){
selectionKey.interestOps(i & (~SelectionKey.OP_WRITE));
}
}3.3 NioServerSocketChannel和NioSocketChannel
NioServerSocketChannel和NioSocketChannel是抽象类NioChannel的一个子类，NioServerSocketChannel和java.nio.channels.ServerSocketChannel的语义是一致的，供服务端使用，绑定指定端口，监听客户端发起的连接请求，并交由相应Handler处理。而NioSocketChannel和java.nio.channels.NioSocketChannel语义一致，作为通信的一个通道。
代码语言：javascript复制public class NioServerSocketChannel extends NioChannel{
private static final Logger LOG = LoggerFactory.getLogger(NioServerSocketChannel.class);
public NioServerSocketChannel(){
super(newSocket());
}
public static ServerSocketChannel newSocket(){
ServerSocketChannel socketChannel = null;
try {
socketChannel = ServerSocketChannel.open();
} catch (IOException e) {
LOG.error("Unexpected exception occur when open ServerSocketChannel");
}
return socketChannel;
}
@Override
public NioChannelSink nioChannelSink() {
return new NioServerSocketChannelSink();
}
class NioServerSocketChannelSink implements NioChannelSink{
//。。。
}
@Override
public void bind(InetSocketAddress remoteAddress) throws Exception {
ServerSocketChannel ssc = (ServerSocketChannel)sc;
ssc.bind(remoteAddress);
}
@Override
public void connect(InetSocketAddress remoteAddress) throws Exception {
throw new UnsupportedOperationException();
}
}这里获取ServerSocketChannel实例的方式是通过ServerSocketChannel.open()，其实也可以通过反射来获取，这样就能将ServerSocketChannel和SocketChannel的实例化逻辑进行统一，我们只需要在实例化Channel的时候将ServerSocketChannel.class 或 SocketChannel.class当作参数传入即可。
NioSocketChannel的实现如下：
代码语言：javascript复制public class NioSocketChannel extends NioChannel{
private static final Logger LOG = LoggerFactory.getLogger(NioSocketChannel.class);
public NioSocketChannel() throws IOException{
super( newSocket());
}
public NioSocketChannel(SocketChannel sc) throws IOException{
super(sc);
}
public static SocketChannel newSocket(){
SocketChannel socketChannel = null;
try {
socketChannel = SocketChannel.open();
} catch (IOException e) {
}
return socketChannel;
}
@Override
public NioChannelSink nioChannelSink() {
return new NioSocketChannelSink();
}
class NioSocketChannelSink implements NioChannelSink{
//。。。
}
@Override
public void bind(InetSocketAddress remoteAddress) throws Exception {
throw new UnsupportedOperationException();
}
@Override
public void connect(InetSocketAddress remoteAddress) throws Exception {
SocketChannel socketChannel = (SocketChannel)sc;
socketChannel.connect(remoteAddress);
}
}3.4 NioServerSocketChannelSink和NioSocketChannelSink
通过上面分析可知，NioChannel的只向上提供了操作接口，而具体的底层读写等功能全部代理给了NioChannelSink完成。接下来分析下NioChannelSink的两个子类NioServerSocketChannelSink和NioSocketChannelSink。
首先再看下NioChannelSink的接口：
代码语言：javascript复制 public interface NioChannelSink{
void doRead();
void doSend();
void sendBuffer(ByteBuffer bb);
void close();
}对于NioChannelSink的两个实现类来说，每个方法所对应的语义如下：
doRead()
- NioServerSocketChannelSink：通过accept()接受客户端的请求。
- NioSocketChannelSink：读取NioChannel中的数据
doSend()
- NioServerSocketChannelSink：不支持。
- NioSocketChannelSink：将缓冲区中数据写入NioChannel
sendBuffer()
- NioServerSocketChannelSink：不支持。
- NioSocketChannelSink：发送数据，其实就是将待发送数据加入缓冲队列中。
close()
- NioServerSocketChannelSink：关闭Channel。
- NioSocketChannelSink：同上。
当然了，作为网络编程中的Channel所提供的功能原比这里要多且复杂，作为学习Demo，这里只实现了最常用的几个功能。
下面看下NioServerSocketChannelSink的实现：
代码语言：javascript复制public class NioServerSocketChannel extends NioChannel{
//。。。
class NioServerSocketChannelSink implements NioChannelSink{
public void doRead() {
try {
ServerSocketChannel ssc = (ServerSocketChannel)sc;
handler.channelRead(NioServerSocketChannel.this,
new NioSocketChannel(ssc.accept()));
if(LOG.isDebugEnabled()){
LOG.debug("Dispatch the SocketChannel to SubReactorPool");
}
} catch (Exception e1) {
e1.printStackTrace();
}
}
public void doSend(){
throw new UnsupportedOperationException();
}
@Override
public void sendBuffer(ByteBuffer bb) {
throw new UnsupportedOperationException();
}
@Override
public void close() {
try {
if(sc != null){
sc.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}// end NioChannelSink
//。。。
}下面是NioSocketChannelSink实现：
代码语言：javascript复制public class NioSocketChannel extends NioChannel{
//。。。
class NioSocketChannelSink implements NioChannelSink{
private static final int MAX_LEN = 1024;
ByteBuffer lenBuffer = ByteBuffer.allocate(4);
ByteBuffer inputBuffer = lenBuffer;
ByteBuffer outputDirectBuffer = ByteBuffer.allocateDirect(1024 * 64);
LinkedBlockingQueue<ByteBuffer> outputQueue = new LinkedBlockingQueue<ByteBuffer>();
public void close(){
//clear buffer
outputDirectBuffer = null;
try {
if(sc != null){
sc.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void doRead() {
SocketChannel socketChannel = (SocketChannel)sc;
int byteSize;
try {
byteSize = socketChannel.read(inputBuffer);
if(byteSize < 0){
LOG.error("Unable to read additional data");
throw new RuntimeException("Unable to read additional data");
}
if(!inputBuffer.hasRemaining()){
if(inputBuffer == lenBuffer){
//read length
lenBuffer.flip();
int len = lenBuffer.getInt();
if(len < 0 || len > MAX_LEN){
throw new IllegalArgumentException("Illegal data length, len:" len);
}
//prepare for receiving data
inputBuffer = ByteBuffer.allocate(len);
inputBuffer.clear();
}else{
//read data
if(inputBuffer.hasRemaining()){
socketChannel.read(inputBuffer);
}
if(!inputBuffer.hasRemaining()){
inputBuffer.flip();
fireChannelRead(inputBuffer);
//clear lenBuffer and waiting for next reading operation
lenBuffer.clear();
inputBuffer = lenBuffer;
}
}
}
} catch (Throwable t) {
if(LOG.isDebugEnabled()){
LOG.debug("Exception :" t);
}
fireExceptionCaught(t);
}
}
public void doSend(){
/**
* write data to channel：
* step 1: write the length of data(occupy 4 byte)
* step 2: data content
*/
try {
if(outputQueue.size() > 0){
ByteBuffer directBuffer = outputDirectBuffer;
directBuffer.clear();
for(ByteBuffer buf : outputQueue){
buf.flip();
if(buf.remaining() > directBuffer.remaining()){
//prevent BufferOverflowException
buf = (ByteBuffer) buf.slice().limit(directBuffer.remaining());
}
//transfers the bytes remaining in buf into directBuffer
int p = buf.position();
directBuffer.put(buf);
//reset position
buf.position(p);
if(!directBuffer.hasRemaining()){
break;
}
}
directBuffer.flip();
int sendSize = ((SocketChannel)sc).write(directBuffer);
while(!outputQueue.isEmpty()){
ByteBuffer buf = outputQueue.peek();
int left = buf.remaining() - sendSize;
if(left > 0){
buf.position(buf.position() sendSize);
break;
}
sendSize -= buf.remaining();
outputQueue.remove();
}
}
synchronized(reactor){
if(outputQueue.size() == 0){
//disable write
disableWrite();
}else{
//enable write
enableWrite();
}
}
} catch (Throwable t) {
fireExceptionCaught(t);
}
}
private ByteBuffer wrapWithHead(ByteBuffer bb){
bb.flip();
lenBuffer.clear();
int len = bb.remaining();
lenBuffer.putInt(len);
ByteBuffer resp = ByteBuffer.allocate(len 4);
lenBuffer.flip();
resp.put(lenBuffer);
resp.put(bb);
return resp;
}
public void sendBuffer(ByteBuffer bb){
try{
synchronized(this){
//wrap ByteBuffer with length header
ByteBuffer wrapped = wrapWithHead(bb);
outputQueue.add(wrapped);
enableWrite();
}
}catch(Exception e){
LOG.error("Unexcepted Exception: ", e);
}
}
}// end NioSocketChannelSink
//。。。
}NioSocketChannelSink中的读写功能在Reactor单线程版本里已经分析过，这里就不再赘述。
3.5 ChannelHandler
ChannelHandler是Reactor框架提供给用户进行自定义的接口。接口提供了常用的接口：
代码语言：javascript复制public interface ChannelHandler {
void channelActive(NioChannel channel);
void channelRead(NioChannel channel, Object msg) throws Exception;
void exceptionCaught(NioChannel channel, Throwable t) throws Exception;
}4. 总结
4.1 软件设计中的一些注意点
时刻紧绷一根弦：资源是有限的
代码语言：javascript复制比如在网络编程中，每建立一个Socket连接都会消耗一定资源，当回话结束后一定要关闭。此外，必须考虑非正常流程时的情况。比如发生异常，可能执行不到关闭资源的操作。 如ReactorPool的实例化过程：
public ReactorPool(int nThreads){
//。。
reactors = new Reactor[nThreads];
for(int i = 0; i < nThreads; i ){
boolean succeed = false;
try{
reactors[i] = new Reactor();
succeed = true;
}catch(Exception e){
throw new IllegalStateException("failed to create a Reactor", e);
}finally{
if (!succeed) {
for (int j = 0; j < i; j ) {
reactors[j].close();
}
}
}
}
}当实例化过程中发送异常时，记得要及时回收已占用资源。
又比如在通信一端接受字节流的时候需要注意对异常码流的处理，避免码流过大而耗尽内存，导致OOM。
并发操作分析
- 这个类是线程安全的吗？
- 这个方法是在哪个线程中执行的？
- 是否是热点区域？
- 是否存在并发修改的可能？
- 并发修改是否可见？
在单线程版的Reactor模型中，所有的逻辑都由Reactor单个线程执行，不存在多线程并发操作的情况，那么在我们添加了线程池workerPool后，情况又会怎么样呢？
一般我们在分析并发性问题，通常的做法是先找到可能被多个线程共同访问的类，再分析下这个类是否是线程安全的。如何判断某个类是否是线程安全的？
- 该类是否是有状态的，无状态的类一定是线程安全的。
- 如果有状态，是否可变。如果一个类状态不可变，那么肯定也是线程安全的。
所谓的状态暂可以简单理解为是否有成员变量，不管是静态成员变量还是普通成员变量。
关于"单一职责"
单一职责原则是面向对象软件设计的基本原则之一，难点在于接口的职责如何划分，而职责的划分又需要具体问题具体考虑。拿本次这个小Demo来说，NioChannel的职责是作为数据传输通道，而通道中数据传输方式可能有很多种，那么这里就抽象出一个NioChannelSink接口负责具体传输方式的实现。
职责粒度的划分需要根据需求好好把控。过粗不利于扩展，过细不利于实现。
后记
长路漫漫。。。继续前进！！！
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